Tap changer switch having gap in creepage path between adjacent stationary contacts



3,238,317 PATH March 1, 1966 E. J. LEHMAN TAP CHANGER SWITCH HAVING GAP IN CREEPAGE BETWEEN ADJACENT STATIONARY CONTACTS 2 Sheets-Sheet 1 Filed Sept. 11, 1965 R m m m Eqgene J Lehman E. J. LEHMAN March 1, 1966 TAP CHANGER SWITCH HAVING GAP IN CREEPAGE PAT BETWEEN ADJACENT STATIONARY CONTACTS 2 Sheets-Sheet 2 Filed Sept. 11, 1963 INVENTOR. A 50567749 J Le/zmazz Y United States Patent Oflice Graw-Edison Company, Milwaukee, Wis., 21: corporation of Delaware Filed Sept. 11, 1963, Ser. N0. 308,124 6 Ciaims. (Cl. 200-) This invention relates to tap changers for electrical transformers and particularly to manually operated, noload, tap changer switches for distribution transformers.

Distribution transformers are often provided with nol-oad tap changer switches which are manually operated through a hand hole in the transformer casing cover, when the transformer is de-energized, to change the voltage ratio of the transformer. Conventionally such tap changer switches are supported on anupper core clamping member and immersed in the oil within the transformer casing. The size of the tap changer switch heretofore necessitated that it be positioned above the transformer core and coil assembly or that the tank be of increased diameter to permit the tap changer switch to be disposed between the core and coil assembly and the tank sidewall. Reduction in size and height of a pole mounted distribution transformer is highly desirable, particularly since reduction in height also results in decrease in the amount of transformer oil and weight of the transformer. Mounting of the tap changer switch above the transformer core and coil assembly increases both the casing height and the amount of oil required to immerse the tap changer switch, but it has hereto-fore been impossible to construct a tap changer switch of sufiiciently small size to permit mounting between the core and coil assembly and the casing sidewall for the purpose of reducing casing height and the amount of transformer oil.

Conventionally such a tap changer switch has a plurality of metallic stationary contacts mounted in circumferentially spaced apart relation in an arc on an insulating support with sufficient spacing to provide the necessary dielectric breakdown strength between adjacent contacts. The dielectric breakdown strength between adjacent stationary contacts and between stationary contacts and ground is a limiting factor in the reduction in size of such a tap changer switch. Electrical breakdown between adjacent stationary contacts and between such contacts and ground usually occurs along the surface of the insulating member which support the stationary contacts, and heretofore it has been impossible to further reduce the creepage distance along the surface of the insulating support and still maintain the necessary breakdown strength between adjacent contacts and between such contacts and ground. Consequently it has heretofore been impossible to further reduce the size of the tap changer switch.

It is an object of the invention to provide a tap changer switch which is substantially smaller than prior art devices. It is a further object of the invention to provide a tap changer switch which is sufficiently small to be mounted between the core and coil assembly and the casing sidewall of even small kva. distribution transformers, thereby permitting reduction in the height of the transformer casing and the amount of oil within the casing.

These and other objects and advantages of the invention will be more readily apparent from the following detailed description when taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a side elevation view of a preferred embodiment of tap changer switch embodying the invention positioned within a distribution transformer casing Patented Mar. 1, 1966 with the transformer elements in section and with portions of the switch broken away to better illustrate the movable contact;

FIG. 2 is a view taken on line 2-2 of FIG. 1;

FIG. 3 is a partial view taken along lines 3-3 of FIG. 1;

FIG. 4 is a partial plan view of an alternative embodiment of the invention; and

FIG. 5 is a partial front view of the embodiment of FIG. 4.

Referring to FIGS. 1 to 3 of the drawing, the tap changer switch 10 of the invention is adapted to be mounted by screws 11 on the web of an upper core clamp channel 12 of the distribution transformer core and coil assembly including a laminated magnetic core 14 which may be of cruciform section and have the upper yoke thereof disposed within the upper core clamp channel 12. The tap changer switch 10 is mounted between the transformer core and coil assembly and the transformer casing sidewall 16 and is immersed in the transformer oil 17 which fills the casing to a level 18 above the core and coil assembly.

The components of the tap changer switch 10 will be described with reference to the horizontal and vertical directions as seen in the drawing, but it will be appreciated that the tap changer switch of the invention can be mounted in any desired position.

Tap changer switch 10 may be manually operated by a handle 19 having a shaft portion 20 provided with a noncircular recess 21 which receives a complementary noncircular projection on a switch operating shaft 22 to provide a driving connection therebetween. Switch operating shaft 22 extends through and is rotatably journalled within registering apertures 23 in vertically spaced apart upper and lower insulating support members 24 and 2a of the tap changer switch 10. Operating shaft 22 is provided with shoulder portions 27 which abut against the upper and lower support members 24 and 26 and prevent axial movement of shaft 22. The operating shaft 22 and the support members 24 and 26 are preferably molded of an insulating material such as alkyd resin provided with a glass fibre filter and having high mechanical strength and high surface resistivity. Operating shaft 22 has an integral radially extending arm 29 provided with a longitudinally extending bore 30.

Upper support member 24 is generally Z-shaped with a generally vertical central portion 31 from the upper end of which a horizontal mounting arm portion 33 extends in overlying relation to the web of upper core clamp channel 12, and from the lower end of which a horizontal contact pin support portion 34 extends in the opposite direction. Screws 11 affix the mounting arm portion 33 and a position indicator 35 of suitable material such as pressboard to the upper core clamp channel 12 and thus support the tap changer switch 10 on the transformer core and coil assembly. Lower support member 26 is generally fiat and positioned horizontally in spaced relation below the contact pin support portion 34 of upper support member 24. Three upwardly extending, horizon tally spaced apart integral posts 36 on lower support member 26 may be joined by suitable means such as epoxy cement to three complementary depending integral posts 37 on upper support member 24 to secure the upper and lower support members 24 and 26 in vertically spaced relation, but the posts 36 and 37 are secured together during assembly only after operating shaft 22 is inserted within the registering apertures 23 in the upper and lower support members 24- and 26 and the contact pressure spring and movable contact are assembled within axial bore 30 in radial arm 29. Posts 36 may have cavities 38 in the end face thereof which receive corresponding projections on the end face of the post 37 to facilitate alignment of the posts as they are joined by epoxy cement. It will be appreciated that the joints between posts 36 and 37 may be at any desired point along the length thereof or that the cavities 38 may be in the upper support member 24 or the lower support member 26, in which case I the entire post will be integral with the opposite support member 24 or 26. Alternatively, the posts may be separate glass fibre filled rods which are joined at their ends to the upper and lower support members 24 and 26.

In the preferred embodiment lower support member 26 has three tooth-like projections 40, 42 and 44 along the front edge thereof arranged in an are having the axis of operating shaft 22 as the center and also having grooves therebetween, and contact pin support portion 34 of upper support member 24 also has three tooth-like projections 41, 43 and 45 arranged in said are along the front edge thereof with grooves therebetween. The tooth-like projections 41, 43 and 45 on upper support member 24 are opposite the grooves between the tooth-like projections 40, 42 and 44 in lower support member 26. In other words, the tooth-like projections 4d, 42 and 44 on lower support member 26 alternate with the tooth-like projections 41, 43 and 45 on upper support member 24. Metallic stationary contact pins are molded within each of the tooth-like projections 40, 41, 42, 43, 44 and 45. The contact pins 47 molded within tooth-like projections 40, 42 and 44 in lower support member 26 extend above the lower support member 26 approximately to upper support member 24 and are disposed opposite the grooves in upper support member 24 and also extend below the lower support member 26 and terminate in a tubular portion 48 within which a tap conductor (not shown) may be crimped. The contact pins 49 molded within toothlike projections 41, 43 and 45 on upper support member 24 only depend from upper support member 24 and extend below the lower support member 26 through the grooves between the tooth-like projections 40, 42 and 44 on lower support member 26 and also terminate in a tubular portion 48 Within which a tap conductor may be crimped.

The contact pins 47 and 49 are thus arranged in circumferentially spaced apart relation in a common plane along an are having the axis of shaft 22 as the center and with contact posts 47 on lower support member 26 alternating with pins 49 on upper support member 24.

A metallic movable contact member 56 having a shank portion 51 telescoped within bore 3%) in radial arm 29 and a hemispherical headed portion 52 adapted to abut against the contact pins 47 and 49 is resiliently urged against the contact pins 47 and 49 by a spring 54 compressed Within bore 30. Headed portion 52 of movable contact member 50 thus sequentially electrically connects adjacent contact pins 47 and 49 when operating handle 19 and operating shaft 22 are rotated to complete the desired tap connections for the transformer and change the transformer voltage ratio.

It will be appreciated that inasmuch as the stationary contacts are alternately mounted on the upper and lower support members 24 and 26 with uniform spacing between stationary contact pins 47 and 49, the electrical breakdown path between adjacent contact pins 47 and 49 includes a creepage path portion along the surface of one of the support members 24 and 26 plus a breakdown path through the high dielectric strength oil 17 in which the tap changer switch 10 is immersed, thereby permitting a reduction in the spacing between stationary contacts in comparison to prior art constructions. The surface resistivily of the insulating material from which the upper and lower support members 24 and 26 are molded permits a still further reduction in spacing between stationary contacts in comparison to prior art tap changer switches constructed of porcelain which has relatively low surface resisitivity.

At the extreme positions of switch rotation, the radial 4 arm 29 abuts against the posts 36 and 37 which join the upper and lower support members 24 and 26 and serve as limit stops to prevent rotation of the movable contact member 50 beyond the tap positions.

The position indicator 35 has an aperture 55 which receives the shaft portion 20 of operating handle 19 and also is provided with a plurality of indicia 56 which cooperate with a pointer 57 on operating handle 19 to visually indicate the position of the tap changer switch 10.

The reduced size of the tape changer switch of the invention is particularly advantageous in distribution transformers below 25 kva. rating wherein space is at a premium. In one small kva. size transformer, the tap changer of the invention permitted the top oil level to be only one half inch above the transformer core and coil assembly in comparison to greater than two inches for prior art tap changers, thereby permitting a material reduction in the amount of oil and in the weight of the transformer.

FIGS. 4 and 5 illustrate an alternative embodiment of the invention which permits elimination of the tooth-like projections with grooves therebetween on one of the support members. As illustrated the tooth-like projections and the grooves therebetween are eliminated on the upper support member 24', and the stationary contact pins 47 molded within tooth-like projections 40, 42 and 46 on lower support member 26 are shorter than the contact pins 49 molded within upper support member 24' but are spaced sufficiently far from upper support member 24' to provide the desired dielectric strength in the breakdown path through the oil 17 between the stationary contact pins 47' and the contact pins 49 and also between the stationary contact pins and ground.

While only two embodiments of the invention have been illustrated and described, many modifications and variations thereof will be readily apparent to those skilled in the art, and consequently it is intended in the appended claims to cover all such variations and modifications which fall within the true spirit and scope of the invention.

I claim:

1. In a tap changer switch, in combination, spaced apart first and second insulating support members, a plurality of circumfe-rentially spaced apart stationary contacts arranged in an arc, and a movable contact rotatable about an axis through the center of said are into sequential engagement with said stationary contacts, said stationary contacts being disposed in a plane common to said movable contact and perpendicular to said axis and oddnumbered stationary contacts being affixed to said first support member and spaced from said second support member and even-numbered contacts being aflixed to said second support member and spaced from said first support member, and means for supporting said movable contact for rotation in said plane about said axis, whereby the electrical breakdown path between adjacent stationary contacts includes a creepage path portion along the surface of one of said insulating support members in series with a portion of said breakdown path through the medium in which said tap changer switch is immersed.

2. A tap changer switch comprising, in combination, spaced apart first and second insulating support members, a plurality of first stationary contacts mounted in circumferentially spaced apart relation along an are on said first support member and being spaced from said second support member, a plurality of second stationary contacts mounted in circumferentially spaced apart relation along said are on said second support member and being spaced from said first support member, and a movable contact rotatable about an axis through the center of said are into sequential engagement with said first and second contacts, said first and second stationary contacts being disposed in alternating relation in a common plane perpendicular to said axis, and means for supporting said movable contact for rotation in said plane about said axis, whereby the electrical breakdown path between adjacent stationary contact members includes a creepage path portion along the surface of one of said support members in series with a portion of said breakdown path through the medium in which said switch is immersed.

3. A tap changer switch in accordance with claim 2 wherein said first support member has openings therethrough between said first stationary contacts and said second stationary contacts extend through said openings.

4. In combination, an insulating dielectric fluid, a tap changer switch immersed in said fluid including spaced apart first and second support members of an insulating material having high surface resistivity, a plurality of circumferentially spaced apart stationary metallic contacts arranged in an arc, and a movable contact, means for supporting said movable contact for rotation about an axis through the center of said arc into sequential engagement with said stationary contacts, said stationary contacts and said movable contact being disposed in a common plane perpendicular to said axis and odd-numbered stationary contacts being mounted on said first support member and spaced from said second support member and even-numbered contacts being mounted on said second support member and spaced from said first support member, whereby the electrical breakdown path between adjacent stationary contacts includes a creepage path portion along the surface of one of said support members in series with a portion of said breakdown path through said insulating fluid.

5. A tap changer switch comprising, in combination, spaced apart first and second insulating support members, a plurality of metallic first stationary contact pins supported in circumferentially spaced apart relation in an are on said first support member, said first support member having openings therethrough between said first stationary contact pins, a plurality of metallic second stationary contact pins supported in circumferentially spaced apart relation on said second support member along said are and being in alternating relation with said first contact pins and extending toward said openings through said first contact member so that a plane intersects all said first and second contact pins, said first pins being spaced from said second support member and said second pins being spaced from said first support member, whereby the electrical breakdown path between adjacent first and second stationary contact pins includes a creepage path portion along the surface of one of said support members in series with a portion of said breakdown path through the medium in which said switch is immersed, and a movable contact rotatable in said plane about an axis perpendicular to said plane through the center of said are into sequential engagement with said first and second stationary contact pins, means for mounting said movable contact for rotation about said axis, and resilient means for urging said movable contact in a radially outward direction against said contact pins.

6. A tap changer switch comprising, in combination, spaced apart first and second insulating support members each having a plurality of tooth-like projections thereon arranged in an arc with grooves between said projections, said tooth-like projections on said first support member being opposite said grooves on said second support member, a plurality of first metallic stationary contact pins supported in circumferentially spaced apart relation on said first support member with each being mounted on one of said projections and extending toward one of said grooves in said second support member and being spaced from said second support member, a plurality of second metallic stationary contact pins supported in circumfe-rentially spaced apart relation on said second support member with each being mounted on one of said projections and extending toward one of said grooves in said first support member and being spaced from said first support member, said first and second stationary contact pins on said first and second support members being disposed in alternating relation in a common plane along a common are, whereby the electrical breakdown path between adjacent stationary contact pins includes a creepage path portion along the surface of one of said insulating support members in series relation with a portion through the medium in which said switch is immersed, and a movable contact rotatable in said plane about an axis perpendicular to said plane through the center of said are into sequential engagement with said stationary contact pins, means for mounting said movable contact for rotation about said axis, and resilient means for urging said movable contact in a radailly outward direction against said contact pins.

References Cited by the Examiner UNITED STATES PATENTS 1,752,213 3/ 1930 Treanor.

1,895,306 1/1933 Barrington.

2,231,627 2/ 1941 Jansen.

2,833,873 5/1958 Jansen.

2,903,530 5/ 1959 Wilson.

2,967,216 1/1961 Zablocki et al. 200-11 X 2,976,476 3/1961 Snowdon 336- X 3,030,460 4/1962 Huetten et a1 20011 KATHLEEN H. CLAFFY, Primary Examiner. BERNARD A. GILHEANY, Examiner. 

1. IN A TRAP CHANGER SWITCH, IN COMBINATION, SPACED APART FIRST AND SECOND INSULATING SUPPORT MEMBERS, A PLURALITY OF CIRCUMFERENTIALLY SPACED APART STATIONARY CONTACTS ARRANGED IN AN ARC, AND A MOVABLE CONTACT ROTATABLE ABOUT AN AXIS THROUGH THE CENTER OF SAID ARC INTO SEQUENTIAL ENGAGEMENT WITH SAID STATIONARY CONTACTS, SAID STATIONARY CONTACTS BEING DISPOSED IN A PLANE COMMON TO SAID MOVABLE CONTACT AND PERPENDICULAR TO SAID AXIS AND ODDNUMBERED STATIONARY CONTACTS BEING AFFIXED TO SAID FIRST SUPPORT MEMBER AND SPACED FROM SAID SECOND SUPPORT MEMBER AND EVEN-NUMBERED CONTACTS BEING AFFIXED TO SAID SECOND SUPPORT MEMBER AND SPACED FROM SAID FIRST SUPPORT MEMBER, AND MEANS FOR SUPPORTING SAID MOVABLE CONTACT FOR ROTATION IN SAID PLANE ABOUT SAID AXIS, WHEREBY THE ELECTRICAL BREAKDOWN PATH BETWEEN ADJACENT STATIONARY CONTACTS INCLUDES A CREEPAGE PATH PORTION ALONG THE SURFACE OF ONE OF SAID INSULATING SUPPORT MEMBERS IN SERIES WITH A PORTION OF SAID BREAKDOWN PATH THROUGH THE MEDIUM IN WHICH SAID TAP CHANGER SWITCH IS IMMERSED. 